Electroacoustic transducer



y N67 s. L. HEIDRICH ELECTROACOUSTIC TRANSDUCER Filed Feb. 1, 1966 (AiII-I'II'I'Ifll (4147,!

wzzw INVEN TOR STEPHEN L. HEIDRICH United States Patent 3,317,000 ELECTROACOUTIC TRANSDUCER Stephen L. Heidrieh, 29 Richmond Drive, Darien, Conn. 06820 Filed Feb. 1, 1966, Ser. No. 524,015 9 Claims. (Cl. 181-31) This is a continuation-in-part application of the co pending patent application, Ser. No. 298,990, filed July 3 1, 1963, now abandoned.

The present invention relates to sound translating devices, in general, and in particular, to electro-acoustic transducers, more popularly known as loud speakers, which consist of a loud speaker motor unit of the dynamic or moving coil type operating an acoustic diaphragm, one side of which acts on an enclosed space known as the loud speaker enclosure.

The loud speaker enclosure provides an acoustical load on a loud speaker diaphragm, which reacts on the loud speaker motor and opposes the applied power more or less, as determined by the acoustical properties of the enclosure.

Loud speaker enclosures are basically of two types, the completely enclosed type, known as the infinite bafile type and the vented enclosure type, known as the reflex type. The present invention is related in particular to the first mentioned type, namely the completely enclosed or infinite baffle type.

A characteristic of the completely enclosed or infinite type of baffle is such that the low frequency response capability is increased with an increase in size of the enclosure, in other Words, with the increase of the acoustic capacitance contained in the enclosure. For a satisfactory bass response of 50 cycles, this requires an enclosed space of approximately times the cubed nominal diameter of the acoustic diaphragm.

, A charasteristic of the completely enclosed or infinite bafile will also obtain good low frequency response with a smaller enclosure by filling the enclosure with fiberglass to an optimum density, thereby increasing the effective response of low frequencies in smaller enclosures. In this manner a satisfactory low frequency response of 50 cycles may be had with an enclosure of approximately 2 /2 times the cubed diameter of the acoustic diaphragms. This method of increasing the effective size acoustically of an enclosure has been exemplified by U.S. Patent No. 2,775,309 to E. M. Villchur.

The quest is ever for smaller and better speakers.

It is, therefore, a principal object of the present inven tion to provide very small loud speakers having a satisfactory wide frequency range of response with an enclosure, operating as an acoustic buffer unit for low frequencies, the cubic contents of which enclosure are less than one times the diameter of the acoustic diaphragm V cubed.

diaphragm is retarded by the acoustical resistance of the fiberglass packing into a time lag, that may be considered 7 analogous to R-C time circuit used in certain electronic devices. The nature of the fiberglass resistance, however, is such, that it is not effective as a means of further lowering the frequency response by means of further increasing its density beyond a certain optimum for a given volume of enclosure.

The present invention provides for a wide range frequency response from a loud speaker unit with an operative acoustic diaphragm mounted in a very small housing or enclosure in which two very small air chambers functioning as air capacitances are interconnected by an extraordinarily high acoustic resistance in the form of a high resistance air duct conductor, which in cooperation with one of the two air capacitances acts as an acoustic resistance-capacitance couple, that reacts favorably to low frequency cycles of compression and decompression that are impressed via the first chamber from the back of a related acoustic diaphragm.

With these and other objects in view which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawings, in which:

FIGURE 1 is an axial section of a loud speaker embodying the feature of the present invention;

FIG. 2 is a front elevation of the loud speaker, the forward portion being partly removed, to show a section on a plane through the first air chamber back of the acoustic diaphgarm; and

FIG. 3 is an axial section of another embodiment of the loud speaker.

Referring now to the drawing and in particular to FIGS. 1 and 2, the electro-acoustic transducer comprises a conventional dynamic loud speaker unit 10 consisting of a conical acoustic diaphragm 11 suspended by a compliant peripheral fiange 12 cemented to a supporting rim 13 of a basket 14 of a magnetic structure 15 actuated by a voice coil 16 which operates in a magnetic gap 17 in the magnetic structure 15. The dynamic loud speaker 10 is integrated in a housing or enclosure according to this acoustic device.

The housing comprehends essentially two cooperative enclosures, namely a first enclosure 18 defining a first chamber 20 disposed on the back of the acoustic diaphragm 11 and a second enclosure 19 defining a second chamber 21 having a peripheral wall 22 overlapping and slightly spaced apart from a peripheral wall 23 of the first enclosure 18, so as to form an air duct 24 between the peripheral walls 22 and 23, respectively, and interconnecting the chambers 20 and 21. A gasket 25', preferably of rubber is disposed about the peripheral walls and the basket 14 or the diaphragm 11.

As clearly disclosed in FIG. 1 of the drawing, the first enclosure 18 comprises the peripheral wall 23 which extends forwardly short of the rim 13 to define a peripheral orifice 25 at the forward edge of the peripheral wall 23 and the magnetic structure 15 is preferably secured to the second enclosure 19 by a screw 26 and thereby holds the first enclosure 18 in fixed and spaced relationship to the back of the loud speaker unit 10, or the first enclosure 18 may be free fitted over the magnetic structure 15, thereby freely suspended in fiberglass packing provided therein. It will also be noted that the peripheral Wall 23 of the first enclosure 18 is contiguous with the peripheral wall 22 of the second enclosure 19, thereby defining a peripheral air duct conductor 24, which interconnects, as stated above, the chamber 20 with the chamber 21.

The chambers 20 and 21 are packed with fiberglass 27 and 28, respectively, to optimum density for suitable damping.

The electro-acoustic transducer operates in the following manner:

The movements of the diaphragm 11 impelled by the energized voice coil 16, generates compressions and decompressions of air in the chamber 20 which being of a small volume causes plus and minus pressures to attain exceptionally high degrees above and below the atmospheric pressure and, thereby, provides an air stiffness and control over the movements of the diaphragm 11, which predominates over the mechanical stiffness of the compliances in the diaphragm 11. The air stiffness thereby takes over much of the inertia of the moving parts.

The air duct conductor 24 slowly releases the higher pressures in the chamber 20, which are generated increasingly with decrease of frequency to the chamber 221, where plus and minus pressures are regenerated again but with a time lag as compared with the pressures prevailing in the first chamber and reach a peak when the incoming air pressures through the air duct conductor 24 becomes equal to the air pressures in the second chamber 21. The regenerated pressures in the chamber 21, which acts as an acoustic butler unit for low frequencies, become immediately resurgent with the reversal of air flow adding the released power of resurgence through this air duct conductor 24 to the back of the acoustic diaphragm 11 at a frequency compatible to that in the acoustic resistance-capacitance couple of the air dutc conductor 24 with the air chamber 21.

Because of the small housing desired for this loud speaker, the acoustic capacitance of the cham bers 20 and 21 is comparatively minute and the complementary acoustic resistance necessary to achieve a low frequency resurgence of 50 cycles or less is extraordinarily great. The high acoustic resistance is achieved in accordance with the present invention by the extremely close contiguous spacing, that is, in the order of a few thousandths of an inch, extending over a range of about one-tenth of a thousandth to about one hundred thousandths of an inch, depending upon the size of the loud speaker, between the peripheral walls 22 and 23 of the enclosures 18 and 19, which define the aid duct conductor 24, thus providing the means for attaining an extraordinarily high acoustic resistance in the great area of surface viscosity provided as compared to the minute cross sectional area of the duct conductor 24.

It is known that loud speakers have heretofore employed acoustical loading systems acting on the back of a related acoustic diaphragm which consists of two air chambers cooperating through an acoustic resistance of one kind or another, but these known structures have employed relatively large low pressure air chambers or capacitances acoustically coupled .to each other through a relatively low acoustic resistance means and in which the acoustic resurgencies were dominated by the properties of the acoustic chambers of capacitances rather, than by the acoustic resistance which has been heretofore utilized merely as a damping element. These are essentially low pressure capacitance controlled systems.

The present invention, however, features the opposite concept, that is, a high pressure by virture of the small capacitances, resistance controlled acoustic loading system in which the acoustic resistance is very great and is an effective retarding element to the interchanging flow of air between two relatively small chambers. The

means of attaining such a high acoustic resistance is the- .utilization in a thin air duct conductor of the viscosity eifect of extensive surface area as compared to the cross sectional area of such air ducts.

The present invention features, therefore, a high pressure resistance controlled regenerative acoustic loading system acting on the back of a related acoustic diaphragm, in which a high acoustic resistance is provided in the great viscosity residing in a thin air duct conductor formed intermediate contiguous wall, ascompared to' the cross sectional area of such air duct conductor.

Referring now again to the drawings, and in particular to FIG. 3, an embodiment is disclosed, which follows substantially the previously disclosed embodiment.

The electro-acoustic transducer comprises again a conventional dynamic loud speaker unit 16 consisting of a conical acoustic diaphragm 11' suspended by a compliant peripheral flange 12' cemented to a supporting rim 13' of a basket 14' of a magnetic structure 15' actuated by a voice coil 16' which operates in a magnetic gap 17 in the magnetic structure 15. The dynamic loud speak- 4- er 10' is integrated in a housing or enclosure according to this acoustic device.

While the magnetic structure 15 is substantially identical with the arrangement in the first embodiment, the housing comprises here a pro-assembled acoustic buffer unit 30 consisting of two cooperative, telescopic closures 18 and 19, namely a first enclosure 18 and a second enclosure 19 defining a chamber 21' disposed in the back of the magnetic structure 15, the first enclosure 18' having a peripheral wall 23 and the second enclosure 19' having a peripheral wall 22, which peripheral walls 22' and 23 overlap and telescope relative to each other. The peripheral walls 22' and 23' are spaced apart, so as to form an air duct 24'. The enclosures 1'8 and 19', defin ing the acoustic buffer unit for low frequencies, are sur rounded by an outer enclosure 29, which is preferably of two separate members, which are sealingly joined together, and which receives the magnetic structure 15', and defines a chamber 20' communicating with the chamber 21 in the same manner as described in the description of the first embodiment.

Whereas the present invention constitutes an improvement in the construction of a small loud spaker and preferred embodiments of the construction have been disclosed, it is to be understood that other embodiments are possible and that the scope of the present invention includes any acoustic device employing an operative acoustic diaphragm, the back of which acts on a system of two small interconnected chambers in which the generated and regenerated acoustical resurgencies from one of the other one controlled by a dominatingly high acoustic resistance in an 'air duct conductor defined by wall surfaces of an extensive area, as compared with the cross sectional area of said duct conductor. It is further understood that the term air is analogous with any fluid medium and the use of lighter or heavier than air fluid mediums in the resistance-capacitance system described, are within the scope of the present invention, which is defined by the objects and the claims.

I claim:

1. An electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, comprising a housing including a wall,

means for generating acoustic pressure variations to a fluid medium within said housing and disposed within an opening in said wall of said housing, said housing comprising a first enclosure defining a first chamber,

a second enclosure defining a second chamber,

a first wall of one of said enclosures being disposed contiguous to a second wall of either one of said enclosures and defining a narrow air duct conductor between said first and second walls,

said first chamber communicating with said second chamber, and

said air duct conductor being of substantial length relative to the distance between said first and second walls.

2. An electro-acoustic transducer comprising a housing including a wall,

means for generating acoustic pressure variations to a fluid medium within said housing and disposed within an opening in said wall of said housing,

said housing defining a first chamber,

an enclosure disposed in said first chamber consisting of two parts and one of said parts having a first wall slightly spaced apart from a second wall of the other of said parts,

both parts jointly defining a second chamber, and

said first wall and said second wall disposed between said chambers and defining a passageway of substantial length relative to the distance between said first and second walls.

3. An electro-acoustic transducer comprising a housing,

means for generating acoustic pressure variations to a fluid medium within said housing and disposed within an opening in a wall of said housing,

a cross wall disposed in and dividing crosswise said housing into two chambers,

a peripheral wall extending from said dividing wall and parallel to a wall of said housing,

an air duct conductor comprising the space between said peripheral wall and said wall of said housing,

said air duct conductor being of substantial length relative to the distance between said walls.

4. The electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 1, wherein said first wall of said first enclosure is disposed contiguous to said second wall of said second enclosure.

5. The electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 1, wherein said first wall of said second enclosure is disposed contiguous to said second wall of said sec-0nd enclosure.

6. The electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 1, wherein said first wall and said second wall constitute peripheral Walls of at least one of said enclosures.

7. An electro-acoustic transducer comprising a housing,

means for generating acoustic pressure variations to a fluid medium within said housing and disposed within an opening in a wall of said housing,

said housing comprising a first enclosure having a first peripheral wall and including a first chamber,

a second enclosure cooperating with said first enclosure and having a second peripheral wall and including a second chamber,

said second peripheral wall substantially parallel to and disposed slightly spacedapart from said first peripheral wall,

said first peripheral wall and said second peripheral wall defining therebetween an air duct conductor and the latter communicating said first enclosure with said second enclosure; and

said air duct conductor being of substantial length rela tive to the distance between said walls.

8. The combination in a housing for a loud speaker covering the back of an associated acoustic diaphragm,

a plural Walled partition within said housing dividing the space in said housing into two chambers,

a first chamber covering the back of said acoustic diaphragm and a second chamber backing up on said first chamber,

the dual walls of said partitions consisting of a rigid first wall forming the back of said first chamber except for a space at the periphery of said chamber,

a rigid second wall forming the back of said second chamber,

said walls being in contiguous relationship to each other forming a thin air space the ends of which being open to said first chamber and to said second chamber,

said air space comprising an air leak connecting said two chambers, and

said air leak having suificient acoustic resistance to act as a brake on the movements of said acoustic diaphragm, when operated at the lower frequencies of the audio spectrum.

9. An acoustic generator comprising,

an operative acoustic diaphragm,

an enclosure on the back of said diaphragm,

a plural walled construction having two substantially parallel walls, and dividing said enclosure into two chambers,

said walls defining an air space intermediate said walls,

said air space being an air conductor open at one end to one of said chambers and open at the other end to the other of said chambers, and

said opposing wall surfaces being extensive in an area as compared to the cross-section of said conductor.

geferences Cited by the Examiner UNITED STATES PATENTS 1,837,755 12/1931 Carlisle et a1 18131 1,901,388 3/1933 Wolff 18l31 2,065,751 12/ 1936 Scheldorf 18131 2,765,864 10/1956 Glenn 181-31 2,766,839 10/1956 Baruch et a1. 181-31 FOREIGN PATENTS 903,995 8/ 1962 Great Britain.

STEPHEN J. TOMSKY, Primary Examiner. 

1. AN ELECTRO-ACOUSTIC TRANSDUCER FOR GENERATING ACOUSTIC PRESSURE VARIATIONS TO A FLUID MEDIUM, COMPRISING A HOUSING INCLUDING A WALL, MEANS FOR GENERATING ACOUSTIC PRESSURE VARIATIONS TO A FLUID MEDIUM WITHIN SAID HOUSING AND DISPOSED WITHIN AN OPENING IN SAID WALL OF SAID HOUSING, SAID HOUSING COMPRISING A FIRST ENCLOSURE DEFINING A FIRST CHAMBER, A SECOND ENCLOSURE DEFINING A SECOND CHAMBER, A FIRST WALL OF ONE OF SAID ENCLOSURES BEING DISPOSED CONTIGUOUS TO A SECOND WALL OF EITHER ONE OF SAID ENCLOSURES AND DEFINING A NARROW AIR DUCT CONDUCTOR BETWEEN SAID FIRST AND SECOND WALLS, SAID FIRST CHAMBER COMMUNICATING WITH SAID SECOND CHAMBER, AND SAID AIR DUCT CONDUCTOR BEING OF SUBSTANTIAL LENGTH RELATIVE TO THE DISTANCE BETWEEN SAID FIRST AND SECOND WALLS. 